A diversity of means have been employed for attempting to improve the impact strength and weld line elongation of polypropylene resins. The use of sulfonated EPDM terpolymers to accomplish these objectives is not mentioned in the literature; however, sulfonated EPDM terpolymers have been blended with polyolefinic resins in an attempt to improve the rheological properties of the sulfonated EPDM terpolymers.
U.S. Pat. No. 3,642,728, herein incorporated by reference, generally refers to the concept of blending a sulfonated elastomeric polymer. However, this patent fails to recognize that improved impact and weld line elongation of polypropylene can be achieved by the use of a critical concentration (5 to 15 parts by weight) of a neutralized sulfonated EPDM terpolymer, wherein the elastomeric polymer must be an EPDM terpolymer and the sulfonate groups must be neutralized with a zinc counterion. For example, the use of a magnesium or barium counterion as well as an organic amine as a counterion will not provide a desirable level of improved impact and weld line elongation. High concentrations of rubber may provide good impact, but stiffness is then too low and the polypropylene is inferior to high density polyethylene.
U.S. Pat. No. 3,974,240 teaches blend compositions of a C.sub.2 to C.sub.4 polyolefinic polymer and a sulfonated elastomeric polymer, wherein the concentration of the polyolefinic thermoplastic is 10 to 90 parts by weight per 100 parts of sulfonated elastomeric and more preferably 20 to 90 and most preferably 30 to 70, wherein the experimental data shows blends of 35 parts by weight of sulfonated elastomer.
U.S. Pat. No. 3,974,241 again teaches blend compositions of a C.sub.2 to C.sub.4 polyolefinic polymer and a sulfonated elastomeric polymer wherein the concentration of the sulfonated elastomer is already greater than the concentration of the polyolefinic thermoplastic.
Both U.S. Pat. No. 3,974,240 and U.S. Pat. No. 3,974,241 fail to teach the critical concentration range of the instant invention of 5 to 15 parts by weight of a sulfonated EPDM terpolymer per 100 parts by weight of the polypropylene resin. Additionally, both of these patents fail to teach the critical selection of an isotactic polypropylene homopolymer having an Mn as measured by GPC of at least 15,000, furthermore, these two patents fail to appreciate the criticality of using only a sulfonated EPDM terpolymer, wherein the sulfonate groups must be neutralized with a zinc counterion and not a magnesium, barium or amine counterion as in U.S. Pat. Nos. 3,974,240 and 3,974,241.
U.S. Pat. Nos. 3,974,240; 3,974,241; and 3,642,728 are all directed to elastomeric systems wherein a polyolefin plastic is added to the thermoplastic in minor proportions in order to modify the rheological properties of the elastomer. The compositions of the instant invention are directed to thermoplastic systems, wherein a sulfonated elastomer is added in minor proportions to the thermoplastic.